Image-guided radiation therapy (IGRT) systems use tumor tracking. With accurate tracking, large margins, which are added to planning target volumes due to respiration, can be eliminated to minimize adverse effects of radiation on healthy tissue. In addition, continuous radiation can shorten the duration of treatment sessions by eliminating respiration gating, and active breathing control (ABC).
Conventional tumor tracking determines the tumor location from internal and external surrogates. For instance, multiple passive (metallic) or active (electromagnetic) fiducial markers can be implanted around tumor to continuously monitor the motion of the tumor using X-ray videos. It is also possible to use a correspondence model for external markers, e.g., chest and abdominal pointers that are visible with optical imaging system, see the related U.S. patent application Ser. No. 13/039,906. Internal fiducial markers to estimate the tumor location indirectly are also possible.
However, implanted fiducial markers have a number of disadvantages. The markers require invasive surgery, can damage healthy tissue, cause collapsed lungs, and can shift causing uncertainty in location. In practice, correlation between the external or internal markers and the tumor location can be violated due to the complexity of human breathing.
A markerless tumor tracking method obtains parametric representations of the motion patterns of multiple surrogate regions to estimate the tumor location. However, that method requires labeling of surrogate regions and ground truth tumor locations for a long period of time for model training.
Another method describes multiple template matching for orthogonal X-ray images, see Mei et al., “Robust visual tracking using L1 minimization,” 2th Inter-national Conference on Computer Vision, IEEE, 1436-1443, 2009. That method uses particle filters, sparse templates and a Bayesian state interference framework. For low-contrast tumor regions where the image quality is low, template matching can fail.
The related U.S. patent application Ser. No. 13/039,906 disclosed a method for locating a moving target object, such as a tumor during radiotherapy, by applying a regression to features selected from 3D motion signals acquired of a patient's skin by a single motion sensor, such as laser scanner or 3D computer tomography.